摘要:

The valence‐bond model, so widely used in chemistry, is equally applicable to transition metal alloys. In contrast to models commonly used by physicists, this model emphasizes the distribution of electrons in real space and the differences in spatial distribution of f and d electrons in contrast to s and p electrons. From the energies of the different electronic configurations that are known for almost all of the gaseous atoms and bonding energies for different types of electrons, one can calculate the energies of the electronic configurations in the metal. Thus Ba, Ta, and W with gaseous ground states s2, d3s2, and d4s2are calculated to have the predominant configurations ds, d4s, and d5s, respectively, in the metal. The determination of the correct electronic configuration in the metal is the keystone to reliable predictions. The bonding energies due to the different types of electrons can be used to readily evaluate thermodynamic data to predict the stable composition range for a given structure, or the crystal structure that is stable at a given composition and temperature, and the effect of pressure, temperature and alloying upon the relative stabilities of different structures as well as the occurrence of magnetism.

ISSN:0094-243X    

DOI:10.1063/1.2946889

出版商:AIP    

年代:1973

数据来源: AIP

摘要:

The physical properties of most metallic elements can be deduced from band calculations based on a knowledge of the potential field of the isolated ions and the observed crystal structure. These detailed computations can be approximated by pseudo‐potential calculations which suppress detail of the atomic core structure and within that simplified framework the relative energy of different simple crystal structures can be accounted for. Furthermore the phonon frequencies can be calculated and any instabilities of the lattice structure detected as imaginary frequencies. Magnetic superstructures may be explained by analogous calculations of the spatially varying static susceptibility. Alloys can be treated by assigning a different pseudo potential to each kind of atom, and despite some difficulties about self‐consistent electron transfer between species, band structures can be evaluated. In some situations where strong compound formation is found, the band structure of the d electrons splits into parts, some of which are completely occupied in a way reminiscent of valence bonded crystals like diamond. Perturbation of simple elemental structures may be a satisfactory approach to the stability of some compounds, but the intercomparison of the energy of formation of unrelated complex structures is still beyond theoretical treatment.

ISSN:0094-243X    

DOI:10.1063/1.2946884

出版商:AIP    

年代:1973

数据来源: AIP

摘要:

A specific model for the origin of ferromagnetism in Fe is assumed which attributes the origin of the ferromagnetism to the indirect coupling of localized d‐like electrons by a small number of itinerant d electrons. We find that about 5% of the d‐electrons are in itinerant d bands; the other 95% being in d‐bands which are sufficiently narrow that they can be considered localized. Band calculations and Fermi surface measurements strongly support such a model. Using this model we give the scaling rules for the three contributions to the hyperfine field at any solute atom in an Fe, Co or Ni matrix and evaluate some of these contributions. The analysis indicates that the CEP curves for 4s electrons of Co and Ni are similar to that measured for Fe. Thus the origin of ferromagnetism in Co and Ni is also assumed to be due to a small fraction of itinerant d electrons in these metals.

ISSN:0094-243X    

DOI:10.1063/1.2946903

出版商:AIP    

年代:1973

数据来源: AIP

摘要:

A surface atom of a d‐transition metal experiences a different environment than its bulk counterpart. The parameter of particular importance to most properties is the position of the resonant d‐level, &egr;d, with respect to the bottom of the continuum, &egr;&Ggr;. A simple estimate of the change in &egr;d‐&egr;&Ggr;at the surface will be given for paramagnetic Ni employing the renormalized atom approach. The hole count, i.e. the number of states per atom of one spin lying between the Fermi level and the top of the d bands, is reduced from the bulk value of 0.3 to approximately 0.2. By analogy with Pd, this suggests that the surface layer might be intrinsically non‐magnetic.

ISSN:0094-243X    

DOI:10.1063/1.2946911

出版商:AIP    

年代:1973

数据来源: AIP

摘要:

The possibility of magnetic surface resonances and spin reversal are explored in a simple model of a transition metal surface. The application of our results to ferromagnetic Nickel is discussed.

ISSN:0094-243X    

DOI:10.1063/1.2946918

出版商:AIP    

年代:1973

数据来源: AIP

ISSN:0094-243X    

DOI:10.1063/1.2946930

出版商:AIP    

年代:1973

数据来源: AIP

摘要:

The transverse branch of the phonon dispersion relations of a single‐Q antiferromagnetic Cr sample have been measured near the zone boundary in the [001] direction (around the H symmetry point). The measurements were made with the phonon wave vector q⇒ both parallel and perpendicular to the spin density wave vector Q⇒ at 200°K and 78°K which are above and below the spin flip temperature. All of the measured dispersion curves displayed anomalies similar to those observed in both the paramagnetic (PM) and multi‐Q antiferromagnetic (AFM) phases. The existence of similar anomalies in the PM and single‐Q AFM phases, which are correlated with prominent features of the Fermi surface, suggests that the Fermi surface for the PM and AFM phases are quite similar. However, in the single‐Q measurements differences were observed in the shape of the anomalies for q⇒ parallel and perpendicular to Q⇒ at both temperatures. These directional differences are assumed to arise from the anisotropy of the Fermi surface introduced by the single‐Q spin density wave.

ISSN:0094-243X    

DOI:10.1063/1.2946934

出版商:AIP    

年代:1973

数据来源: AIP

摘要:

Measurements of dHvA oscillations in hcp cobalt spheres are reported and compared with Fermi surface models. Recent observations of dHvA signals in hcp cobalt whiskers are also described.

ISSN:0094-243X    

DOI:10.1063/1.2946939

出版商:AIP    

年代:1973

数据来源: AIP

摘要:

We present a numerical investigation of the role of spin‐orbit coupling in Pd as pertained to the electron spin resonance experiment. For the band structure calculation, we use the modified interpolation scheme of Mueller. The effective g‐value and resonance line shape are calculated for the cases of assumed d‐c magnetic fields in the [100] and the [111] directions. Due to the deviation of the g‐value from its free electron value of 2.0, the resonance line shape has a width of about 25% of the central frequency. The effective g‐value is in fair agreement with the extrapolated value obtained from electron spin resonance experiments in Pd alloys with ferromagnetic elements.

ISSN:0094-243X    

DOI:10.1063/1.2946951

出版商:AIP    

年代:1973

数据来源: AIP

摘要:

In our study of the electron energy bands of ferromagnetic and paramagnetic iron we have found an explanation of the isomer shift anomaly in Fe near its Curie temperature (770°C) which seem to be the natural way of accounting for this phenomena. It was shown that 0.2 electrons in the Van Hove singularity of the majority spin band are removed from this singularity just below 770°C. 10% of these electrons go preferentially into conduction‐like states thus increasing the Isomer shift by the amount found experimentally. The magnetic specific heat of iron and other consequences of this explanation are discussed.

ISSN:0094-243X    

DOI:10.1063/1.2946968

出版商:AIP    

年代:1973

数据来源: AIP